Posts » Bad ideas have long echoes

Quantum stateIt is hard to believe that the interpretation of quantum mechanics is still controversial, but it is. I think part of the problem is that it can be hard to get rid of bad ideas. If a bad idea gets read and written faster than the brains that lie between those steps educate themselves, the idea just keeps reverberating. Take for example the idea of "wave function collapse". A bunch of people believe, who knows why, that somewhere between their brain and a system they are measuring, something magical happens that converts that system from what it is (quantum) to what they'd like it to be (classical). It is hard to understand why this idea is so popular. The math of how a quantum system evolves is perfectly simple, and doesn't need this voodoo. We know that if we take a system of 1000 particles that are in a superposition of two particular states, and then throw away one of the particles somewhere where we won't find it again, the remaining 999 particles will act just like they are now either in one of the states or the other. We go from something strange (superposition) to normal (probability) just by losing control of one particle. The same thing would happen if we just had uncontrolled interactions between the particles and their environment. This "quantum decoherence" is real magic; it plays by rules that are simple, obvious, and very easy to understand step by step, yet it still manages to do something amazing. At the time of writing, Wikipedia claims this idea is winning. I hope so.

If you don't know what I'm talking about, but would like to, do yourself a favor. Pick up a textbook and learn how to use the partial trace. Forget all the words people have been spouting and just look at the math. Then draw your own conclusion. I think you'll find it's very clear what's going on.